Summary
This study presents the whole body and knee three dimensional biomechanics of ACL injuries in football (soccer) player using the model-based image-matching tecnique. We described joint biomechanics (kinematics) of ACL injuries, with a focus, but not limites, to the knee, that showed knee valgus coupled with external and then internal rotation. Biomechanics is also influenced by the ACL patterns.
Abstract
TITLE: Whole body and knee three dimensional biomechanics of ACL injuries in male professional football (soccer) players
AUTHOR(S): Francesco Della Villa, Matteo Zago
Introduction
The Model-Based Image-Matching (MBIM) technique enables the realistic reconstruction of 3D joint kinematics from real-world video footage, holding the potential to unveil time-dependent and multiplanar biomechanics of ACL injuries that remain unclear with traditional methods.
Methods
Thirty-three non-contact and indirect-contact ACL injuries occurred in the main European Leagues and in Major League Soccer (seasons 2020 to 2022) were analyzed: (I) multi-view non-coaxial television images were inspected to identify the Initial ground Contact (IC); (II) camera views were taken every 100 ms from 500 ms before IC to 200 ms after IF; (III) a size-matched pitch was modelled within Blender (v. 3.3, Blender Foundation, The Netherlands) and used to calibrate the cameras by matching reference items in the images; (IV) a 66-degrees-of-freedom 3D skeletal model was matched to fit the player’s pose in each frame/view; (V) poses were interpolated (Bezier spline), and (VI) Euler’s joint angles of the injured limb were extracted.
Results
The knee joint at initial contact (IC) was in a slightly flexed position (41.9° ± 21.5°); at IC+40 ms, the knee flexion increased to 45.9° ± 21.7° degrees. Starting from 100 ms before IC, the knee presents an abduction angle of 2.0° ± 5.0° at IC which increased to over 6° at IC+100 ms. Notably, we observed a knee external rotation (ER) shifting on average from 1.7° to almost 4° (rotation speed of about 40 °/s), followed by a sudden internal rotation (IR) up to about 0°. Concerning the other joints, at IC, the hip was flexed at -35.0 ± 19.4° and abducted at 30.6 ± 13.4°. For the ankle, at IC, there was a plantarflexion of 5.2 ± 14.1°, a slight pronation and internal rotation. Regarding the trunk at IC, we observed a flexion of 15.1 ± 11.9° and a tilt of 5.4 ± 12.5° towards the injured side, along with a rotation of 4.6 ± 20.8° towards the non-injured side. At IC+40 ms, trunk flexion increased to 17.4° ± 12.5°, the tilt towards the injured side also increased to 7.9 ± 13.2°, and the rotation towards the non-injured side increased to 7.4 ± 21.0°.
Discussion
Biomechanics of ACL injuries in football suggests a role of frontal and transverse plane mechanics of the trunk and hip complex, namely an ipsilateral trunk tilt coupled with hip abduction at IC. The results at the knee level confirm the pivotal role of dynamic knee valgus loading. When accepting ground force reaction (GFR) the hip rotates internally while the knee rotates externally. At the same time knee valgus (abduction) progressively increase. Suddenly, there is a transition to knee IR. This is likely due to the compression of the lateral compartment that favors the posterior slide of the lateral femoral condyle thus determining a relative knee IR. We can speculate that this rapid transition from ER to IR is the likely moment of the ACL rupture. These results vary with the mechanisms (noncontact vs indirect contact) and the situational patterns (e.g. pressing vs regaining balance after kicking) of ACL injuries in football players. Therefore, it is important to consider the whole context.
Conclusion
The knee joint kinematics during ACL injuries demonstrate a consistent pattern characterized by swallow flexion, valgus shift and an external followed by internal rotation. This information can be used to inform clinical practice and optimize our prevention and treatment algorithm.